1. Field of the Invention
The present invention relates to a printed wiring board suitable for use in electronic equipment, electrical equipment, a computer, telecommunications equipment, etc. More specifically, it relates to a printed wiring board used for a pin grid array, a ball grid array, a chip size package, MCM, etc., which mounts a semiconductor.
2. Description of the Related Art
A high density of a printed wiring board is required in accordance with high integration of a semiconductor. Particularly, not only an increase in the number of layers and a fine line of a wiring pattern but also a decrease in the size of a plated penetrating through hole are rapidly advancing with regard to a semiconductor-mounting printed wiring board used in the above fields. The decrease in the through hole size can contribute an improvement in the density of a wiring pattern, since it can decrease the size of a pad for the through hole. However, a through hole land and a ball pad and/or a bump pad are disposed separately, so that there is a limit to the density increase. Further, with regard to a conventional cylindrical through hole, the hole is filled with an insulating resin or an electrically conductive paste for preventing an influence on parts to be mounted. However, there have been arising some problems such as sink or falling-off of the filling resin and moisture permeation. For solving the above problems, the present inventors have proposed a printed wiring board having a taper-shaped through hole obtained by plating an internal wall surface and a small-diameter side end of a taper-shaped penetration hole to plate the internal wall surface and seal the small-diameter side end (JP-A-2000-77568, JP-A-2000-77809).
However, the above printed wiring board does not overcome the problem of high density of a wiring pattern.
Generally, a ball pad or a bump pad is disposed separately from a through hole land, and these are connected to each other. When the through hole land can be directly used as a ball pad or a bump pad, a further high density can be actualized. However, for utilizing a through hole part as a ball pad or a bump pad, it is required to carry out lid-plating after filling the through hole with a resin. The above process of resin-filling and lid-plating requires a number of steps and, in addition, the thickness of copper on an external layer becomes large, so that it is difficult to make a fine wiring. Further, with regard to a general through hole, it is difficult to fill it by plating.
In the present fields, there is a tendency to a narrow pitch or a multi-row arrangement of ball pads or bump pads for achieving a further high density. In this case, it is required to arrange a number of wirings between through hole lands. However, the space between through holes is limited so that it is impossible to secure a necessary number of wirings.